Procedure and apparatus for the optimized manufacture of coil springs on automatic spring winding machines

ABSTRACT

Procedure and apparatus for the optimized manufacture of coil springs on automatic spring winding machines. It is the object of the present invention to offer both a procedure and an apparatus by which even in case of fluctuating values of the wire parameters high accuracies during the spring manufacture are guaranteed and simultaneously the scrap is minimized. The solution to this problem is that prior to the winding the wire parameters are determined and the measuring results are used directly for the adjustment of the position of the winding pins or winding rollers and/or the pitch wedge, and that the wire between the uncoiling device and the guiding assembly forms a loop whereby the lateral deflection of this wire loop is measured by a recognition unit and the uncoiling device carries out an additional movement controlled by the recognition unit. The invention is suitable for continuous inspection and correction of errors occurring on spring wires for the optimized manufacture of coil springs on automatic spring winding machines.

DESCRIPTION

The invention relates to a procedure and an apparatus for continuousinspection and correction of errors occurring on spring wires destinatedfor optimized manufacture of coil springs on automatic spring windingmachines, whereby a wire is uncoiled by an uncoiling device in which aspool or coil is provided, and fed into a forming apparatus by means ofa separate feeding device containing winding pins or rollers.

Coil springs must meet steadily increasing accuracy requirements ofindustrial users with regard to their compliance with constructionallyfixed spring parameters, especially the characteristic curve of thespring. The reasons for this are in particular the increasingrequirements for machines and apparatuses in which coil springs areused, as well as the growing degree of automation in the manufacture ofmachines and apparatuses with the trend to limit the work to componentswith narrow tolerances.

The spring wire as basic material is subject to fluctuations dependingon material, geometry, and processing technology. Said fluctuationsbecome visible by deviations of the wire diameter, the mechanicalstrength properties or the material parameters from their nominal valuesand by twists as a result of elastic torsion stress. In addition, adecisive role is played by deviations resulting from the plastic-elasticdeformation behaviour of the spring wire having its origin mostly inprevious manufacturing stages.

The abovementioned fluctuations cause considerable deviations of theparameters of the cold-formed coil spring from the fixed constructionaldata, the effects of which can be seen in deviations of the springcharacteristic curve from the desired characteristic curve.

In particular, the fluctuating thickness of the wire diameter causesinclination changes of the spring characteristic curve, i.e.fluctuations of the spring rate, and the different elastic torsionstresses in the wire coil cause length fluctuations of the producedspring and thus parallel displacements of the spring characteristiccurve.

Inevitably, this leads to scrap during spring production which may beconsiderably high when the springs are of small dimensions and must meethigh accuracy requirements. Since said scrap in most cases is stated notbefore the spring is completed, considerable economic losses arise.Moreover, the necessary supplementary requirements of material andenergy are additional threats to the environment.

The state of the art discloses machines for spring production providedwith intake rollers, mechanically or electrically controlled windingpins or rollers, pitch tools and forming tools. First they weredeveloped mainly with the aim to produce highest possible numbers ofpieces and to guarantee the conversion to the production of springs withdifferent dimensions and forms at justifiable costs.

The state of the art further discloses machines with supervisory andquality assurance systems in which the spring length is measured orinspected mechanically, optically, capacitively or by induction change.

Further, other systems are known which recognize and sort out scrapsprings with the help of said measuring or inspection facilities andwhich automatically correct the control of the automatic spring windingmachine. As a rule, this is carried out based on methods for statisticalprocess control. Other existing variations furnish error signals to theoperator via dialog systems when the finished springs have deviations,so that the operator has to intervene by correcting the control.Further, other systems are known which interrupt the manufacturingprocess after a certain number of scrap springs produced in succession.

JP 55-153 633 (A) discloses a configuration designed to preventtorsional stress of a steel rope during unwinding from a coil by acontrolled turn of the unwinding coil. Hereby said turn of the unwindingcoil is scanned by a sensor which controls the turning movement of afixed run-off roller over which the rope is guided. This configurationcan not be used to determine and to influence the torsional stressesimpressed in a rigid wire.

DE 35 38 944 describes a machine for the production of coil springs bywinding, by which springs with a constantly changeable pitch can beproduced. It is foreseen that the spring manufacturing machine containsan electronic control circuit. A data storing unit stores datadisplaying preselected spring parameters, like for example pitch,length, and diameter. During forming of a spring the respectivepreselected parameter of the spring is monitored, and a signal showingthe monitored parameter is created. The electronically stored data andthe monitoring signal are compared with each other. The springproduction can then be changed according to this comparison for themanufacture of a spring with the preselected parameter. This machinemakes it possible to freely change the parameters of the coil springs inorder to meet the preselected spring requirements. The dimensions of thespring can be changed during the actual manufacturing process of thecoil springs so that springs with pitches can be produced which arechanging continuously over the length of the spring.

This is a manufacturing procedure in which the springs are formed by awinding process around a mandrel. This kind of manufacture allows nochange of the winding diameter. In addition, single wire rods in afinite length are fed, so that no continuous influencing of the wireparameters is possible. Here it is possible to determine and to changethe spring winding parameters, but it is not possible to compensatetolerances of the spring material parameters during the continuousoperation of an automatized spring winding production.

It is the disadvantage of the known spring winding machines andprocedures that they detect any fluctuation of the parameters of thebasic spring wire material not before the production is completed.

It is the object of this invention to find both a procedure and anapparatus of the kind stated at the beginning which guarantee highaccuracies for the spring manufacture even in case of fluctuating wireparameter values, and which simultaneously minimize the scrap.

The solution according to this invention is a procedure and an apparatusas described in claims 1, 2, and 4. The subclaims describe advantageousembodiments.

The procedure according to this invention and the apparatus according tothis invention excel by a number of advantages.

Both the procedure and the apparatus according to this invention make itpossible to compensate the elastic torsion stresses of the spring wire,what is particularly important for the use of springy wire types. Saidtorsion stress is not visible from outside, since after thismanufacturing procedure the hard drawn wire is coiled under tension. Thetorsion stresses are released when this compulsion is taken away fromthe spring wire. They manifest themselves by spreading or turning downof the wire loops and lead to length fluctuations of the produced springand thus to the abovementioned parallel displacement of the springcharacteristic curve.

Measuring of the spring wire diameter in one or two planes can beeffected by several procedures. Measuring in two planes makes itpossible to recognize deviations of the wire diameter and to pass themon to the process control. Besides electric contact or non-contactsensors, optical sensors are advantageous with photometric evaluation ofthe changes.

Correction of the wire diameter fluctuations is particularly importantfor quenched and tempered spring wires. The tensions of these wiresgenerated during drawing are reduced by the final hardening processcarried out at over 860° C., but in exchange, in the interior of thefurnace the wire will be stretched with a tapering effect even at theslightest hindrance of the wire run-off reel. So here fluctuations ofthe wire diameter are considerably more distinctive than in case ofpatented drawn wires and rustproof wires.

By combinating the winding tools with load-sensing instruments itbecomes possible to measure the forming forces of the spring winding andto draw conclusions from their evaluation for the changes of the springparameters, and to include these changes into the machine control.

Another special design includes an E or G module measuring device. Saidmeasuring device consists of rollers causing a slight elasticdeformation of the wire by defined values, meanwhile they measure thenecessary deformation forces.

Since the starting condition of the wire is determined already prior tothe forming process and is taken into account in the control of thewinding tools, the scrap can be considerably reduced.

In addition, the forming result can be constantly supervised and thedesired/actual deviation can be returned to the tool position over aregulator. This leads to considerable reductions of the costs for wages,material, and energy, and to reduced expenses for material recycling andto a reduction of additional enviromental threats.

Both the procedure and the apparatus according to the invention can beadvantageously applied to the production of new automatic springmanufacturing machines, whereby their application is not restricted toautomatic coil spring winding machines, but is also suitable for othermachines for spring production. They are also suitable for subsequentinstallation in already existing numerically controlled automatic springwinding machines so that as many as possible spring manufacturers canbenefit from the invention without fundamental renewal of theirmachinery and with low financial expenditure.

With the help of the gathered measuring results it is further possibleto sort the springs according to different quality classes.

In the following, the invention will be explained in detail by way ofexample in a preferred embodiment with reference to the attacheddrawings in which

FIG. 1 shows a schematic view of the feeding device with loose loop;

FIG. 2 shows an embodiment according to FIG. 1 in which wire straingauges are used as sensors;

FIG. 3 shows a feeding device with rotatable wire pull-off guide;

FIG. 4 shows a schematic view of the apparatus according to theinvention;

FIGS. 5 and 6 show the arrangement for the determination of the springdiameter; and

FIG. 7 shows the linkage of the different components with the help of abloc diagram.

In FIG. 1 the wire is pulled down over the wire feed rollers R from acoil C sitting on a reel. Said reel is driven by a not shown controlleddrive. For the purpose of uncoiling, said reel with coil C is providedin bearings L1 and L2. The complete uncoiling device A is pivotable bymeans of bearing L3. The axis of bearing L3 coincides with the directionof the pulled-off wire D. The wire is fed by the guiding assembly Z overthe recognition unit E towards the wire feeding device of the machine.Under the effect of gravity the wire forms a loop S between the guidingassembly Z and the uncoiling device A. The length of said loop S iscontrolled by the movements of the uncoiling device A and the guidingassembly Z in such a way that it maintains an approximatively constantdiameter. The formation of the loop is supported by the guide rollersFR. When wire D has no torsion stress, wire loop S is hanging verticallydownwards. When the wire has torsion stress, the wire loop S leaves itsvertical position. The degree of this deflection is determined by therecognition unit E1 and leads over a separate control unit to a turn ofthe uncoiling device A in bearing L3 so that the torsion stress iseliminated and can have no effect on the subsequent operations. A secondrecognition unit E2 is provided between machine and wire loop S. Itdetermines the actual wire need for the spring manufacture and controlsthe drives of guide rollers R and bearings L1, L2 depending on thecorresponding wire need. In the example shown in the drawing the slackof the wire concerned is determined for this purpose.

FIG. 2 shows a possibility to arrange the sensors. In this case twosensor rollers SR are located at the wire loop S which are fixed to therack by springs F1 and F2. If wire D is under torsion stress, thislatter causes a deflection of wire loop S and thus also a deflection ofsprings F1 and F2. The springs F1 and F2 are equipped with wire straingauges DMS by which the deflection is measured. With the help of saidwire strain gauges DMS a size value for the deflection of the wire loopS can be determined and the necessary swivel movement of the uncoilingdevice A can be controlled.

Besides the installation of wire strain gauges, different other sensorscan be used for the recognition unit. The sensors can on the one handdetermine the deformation of a plastic element, like this is shown inFIG. 2, and on the other hand measure the displacement of an element bya path-measuring system. In the most simple case stops on both sides aresufficient which signalize contact when they are touched.

FIG. 3 shows a feeding device with pivoted wire pull-off guide DF. Herethe torsion stressed wire is pulled down from a reel H under tension.The torsion stressed wire is guided within the realization unit E1around a pivoted wheel in a wire loop acting as torsion indicator. Forthis purpose said wheel is so installed that it can make a swivelmovement around an axis vertical to its wheel axis, in addition to itsturn around the wheel axis caused by the pull-off movement of the wire.Said swivel movement depends on the torsion stress contained in the fedwire. The recognition unit E1 is connected with a sensor SE whichindicates the deflection of the recognition unit E1. Therefore, anytorsion stress between the fixed guiding wheel L and the wire pull-offguide DF leads to a deflection of recognition unit E1 and is indicatedby the sensor. When torsion-free wire is uncoiled, the reel cup mustcarry out a 360° turn to uncoil one complete wire loop. The torsionstresses are eliminated by introduction of a defined relative movementbetween the reel and the controllably pivoted wire pull-off guide DF sothat a twist-free wire is fed to the winding machine. Particularlyadvantageous is here, that this arrangement allows a quick and preciseexecution of the controllable additional movement of the wire pull-offguide DF. This is obtained especially by the fact that the movement ofthe wire pull-off guide DF which has only very little mass is separatedfrom the movement of the reel H. The reel H, too, which has much mass,must effect an additional movement in order to guarantee a continuouswire outlet. The additionally pivoted wire pull-off guide DF allowsseparation of these two movements so that it is not necessary toaccelerate the reel H with strong forces and consequently high wear ofthe moving parts.

FIG. 4 shows a schematic illustration of the apparatus according to theinvention. For the production of a coil spring the wire is first ledpast a wire diameter measuring device 1 by which the actual diameter ofthe spring wire is determined. Thereafter the wire passes into themeasuring device where the E or G module are determined. This measuringdevice consists of rollers 2. Among said rollers at least the roller 2.3is adjustable in vertical direction to the roller axis, roller pair 2.2is driven, and roller pair 2.1 is running freely. The abovementionedadjustment causes an elastic deformation of the wire by defined values.The rollers are connected to sensors which continuously measure thebearing loads N1, N2, and N3. Said bearing loads depend on the materialproperties of the spring wire and allow the determination of the Emodule. By this it becomes possible to determine the G module for therespective actual state. In order to carry out the measurementindependent from the influences of the machine function, loops 4.1 and4.2 are provided. The deformation properties of the wire to be processedcan be recognized and suitable reactions can be started. Such reactionscan be for example an alarm signal or the release of appropriateadjustment movements of the forming tools. When the wire has passedthrough this device, it goes over the intake guide EF into the guidingassembly Z and then into the forming device. The adjustment of thewinding pins for the wire thickness depending control of the springdiameter is carried out on the basis of the following formula: ##EQU1##

Explanations

D_(mk) =mean spring diameter after correction

D_(mo) =desired value of mean spring diameter

d_(ist) =determined actual value of the wire diameter

d_(o) =desired value (standard value)

The intake guide EF leads the wire D in a defined bow towards theforming device. Said intake guide EF is effective when the wire is bentand guarantees definite winding conditions. The intake guide EF canconsist of a curved pipe or be formed by an arrangement of rollers.

With regard to the forming device, FIG. 4 shows the winding pins 3.1 and3.2 which are electrically adjustable. Another adjusting device allowsadjustment of the pitch wedge so that all geometric parameters of thespring to be produced can be influenced. The winding pins 3.1 and 3.2are provided with force sensors by which the winding forces N4 and N5are continuously determined. By this also changes of the wire formingproperties are detected and transmitted to the process control forevaluation.

FIGS. 5 and 6 show an arrangement with which the outside spring diameterD_(a) and the pitch P can be determined after the winding. Regarding theappropriate measuring device for this, different solutions are possible.As shown in the example, the spring diameter is determined at the spring5 with the help of a CCD matrix 6. Hereby the spring 5 is in definitetouch with the V groove 7. Fluctuations of the spring diameter can alsobe stated in a known manner by the silhouette procedure or the scanningprinciple with optical measuring devices.

FIG. 7 is a schematic illustration of the linkage of the structuralcomponents. The required adjusting movements are triggered by a computerconnected with each of the measuring stations of the machine via signalprocessing. Hereby the wire is drawn into the device by the wire intake.Prior to this it passes through the wire diameter measuring device DDME.The wire intake is in a known manner connected to a path-measuringdevice from which a signal for the length of the wire to be processed isgathered. This measuring device is not shown on the drawing. Prior tothe wire intake the apparatus according to the invention has an E or Gmodule measuring device E/G-ME with a force measuring device KME and apath-measuring device WME with which the deformation of the wire and thenecessary force are determined. Based on both the determined force anddeformation values, the actual values for the E module of the wire canbe determined. The G module can be determined with the help of the Emodule. When the wire has passed through the measuring device, it is fedto the intake device and thus to the forming device in which the windingpins 3 and the pitch wedge are contained. Winding pins 3 and pitch wedgeeach are connected with linear drives with which the actually necessarypositions of these elements are approached. In addition, the windingpins 3 are connected with a force measuring device KME which transmitsinformation on the measured forming forces to the signal processing forevaluation. When the wire has passed through the forming device it isshaped as a spring. The dimensions of this spring body are determined bythe outside diameter measuring device ADME and the pitch measuringdevice SME. The spring body is cut off in the required length by meansof a cutting-off knife controlled by the signal processing. The thusobtained spring is evaluated by a length measuring device LME and aforce measuring device KME in a way that the characteristic curve of thespring is determined. The so gathered actual data are also transmittedto the signal processing. The measurement of the spring length by thelength measuring device LME and of the spring forces by the forcemeasuring device KME and consequently the determination of the springcharacteristic curve can also be carried out before the spring iscut-off.

Due to this arrangement it is possible to measure deviations of thespring wire diameter and to realize appropriate compensations as well astheir effects on the pitch of the spring characteristic curves bycontrolled change of other spring parameters, preferrably of the springdiameter. Since the actual value of the sliding module is also measured,it is possible to gather a number of further correction information forthe maintenance of the spring characteristic curve and to take them intoaccount for the adjustment movements.

List of Reference Numbers

1 wire diameter measuring device

2 rollers

3 winding pins

4 wire loops

5 spring

6 CCD matrix

7 V groove

N1, N2, N3 reaction forces

N4, N5 winding forces

F spring

P pitch

D_(a) outside spring diameter

MS wire strain gauge

DDME wire diameter measuring device

ADME outside diameter measuring device

SME pitch measuring device

LME length measuring device

KME force measuring device

WME angle measuring device

E/G-ME E or G module measuring device

z guiding assembly

L guiding wheel

H reel

S wire loop

DF wire pull-off guide

EF intake guide

C coil

SP spool

D wire

A uncoiling device

R rollers

L1, L2, L3 bearings

FR guide rollers

SR sensor rollers

We claim:
 1. A procedure for winding coil springs out of wire which isuncoiled by an uncoiling device and fed by means of a separate guidingassembly to a forming device for winding the wire in helical shape,wherein prior to the winding at least one wire parameter is determinedand the measuring results are directly used for controlling the formingdevice, and based on the deviation of the wire diameter from its desiredvalue, determined prior to winding, the forming device is controlled insuch a way that the spring diameter is ##EQU2## whereby D_(mk) signifiesmean spring diameter after the correctionD_(o) signifies desired valueof the mean spring diameter d_(ist) signifies mean actual value of thewire diameter and d_(o) signifies desired value (standard value) of thewire diameter.
 2. A procedure according to claim 1, wherein the uncoiledwire has elastic torsional stresses before winding, the wire between theuncoiling device and the guiding assembly is guided in a loop wherebyany lateral deflection of the wire loop is measured by a recognitionunit; and wherein the uncoiling device in addition to the rotationmovement for uncoiling the wire makes another movement the extent andthe direction of which are controlled by the recognition unit in such away that the torsional stresses are compensated.
 3. A procedure forwinding coil springs out of wire which is uncoiled by an uncoilingdevice and fed by means of a separate guiding assembly to a formingdevice for winding the wire in helical shape, wherein prior to thewinding at least one wire parameter is determined and the measuringresults are directly used for controlling the forming device, andwherein as said wire parameter at least one of the modulus of elasticityand the modulus of transverse elasticity of the wire to be wound isdetermined.
 4. A procedure according to claim 3, wherein the uncoiledwire has elastic torsional stresses before winding, the wire between theuncoiling device and the guiding assembly is guided in a loop wherebyany lateral deflection of the wire loop is measured by a recognitionunit; and wherein the uncoiling device in addition to the rotationmovement for uncoiling the wire makes another movement the extent andthe direction of which are controlled by the recognition unit in such away that the torsional stresses are compensated.
 5. A procedure forwinding coil springs out of wire which is uncoiled by an uncoilingdevice and fed by means of a separate guiding assembly to a formingdevice for winding the wire in helical shape, wherein prior to thewinding at least one wire parameter is determined and the measuringresults are directly used for controlling the forming device, andwherein the uncoiled wire has elastic torsional stresses before winding,the wire between the uncoiling device and the guiding assembly is guidedin a loop whereby any lateral deflection of the wire loop is measured bya recognition unit; and wherein the uncoiling device in addition to therotation movement for uncoiling the wire makes another movement theextent and the direction of which are controlled by the recognition unitin such a way that the torsional stresses are compensated.
 6. Anapparatus for winding coil springs out of wire which is uncoiled by anuncoiling device and fed by means of a separate guiding assembly to aforming device for winding the wire in helical shape, wherein at leastone winding parameter is determined and the measuring results aredirectly used for controlling the forming device, said apparatuscomprising the uncoiling device for uncoiling the wire from a spool or acoil, and the guiding assembly for feeding the wire towards a formingdevice for the winding of said wire, characterized by the formation of aloop of the wire between the uncoiling device and the guiding assembly,by a recognition unit located next to said loop for measuring a lateraldeflection of the wire loop, and by a wire pull-off guide of theuncoiling device arranged rotatably around the spool or coil axis andcontrolled by the recognition unit to carry out an additional movement.7. An apparatus according to claim 6, wherein the recognition unitcomprises a roller which takes up the wire loop and which isadditionally swivel-mounted on an axis parallel to the wire guidingdirection, as well as a sensor which produces a signal depending on thedeflection of the roller swivelling about said axis.
 8. An apparatusaccording to claim 6, wherein a wire diameter measuring device isprovided between the uncoiling device and the guiding assembly.
 9. Anapparatus according to claim 6, wherein a measuring device for thedetermination of at least one of the modulus of elasticity and themodulus of transverse elasticity of the wire is provided between theuncoiling device and the guiding assembly.
 10. An apparatus according toclaim 9, wherein the measuring device has rollers which cause an elasticdeformation of the wire by defined values whereby it measuresdeformation forces and deformation paths.
 11. An apparatus according toclaim 6, wherein force sensors for the determination of deformationforces created by winding pins or rollers of the forming device areprovided at the winding pins or rollers.
 12. An apparatus according toclaim 6, wherein the forming device has one measuring device each formeasuring an outside diameter of the spring and a pitch of the woundspring, respectively.
 13. An apparatus according to claim 6, wherein anintake guide is provided between the uncoiling device and the guidingassembly and the wire is guided by said intake guide in a defined bowtowards the forming device.
 14. An apparatus for winding coil springsout of wire which is uncoiled by an uncoiling device and fed by means ofa separate guiding assembly to a forming device for winding the wire inhelical shape, wherein at least one winding parameter is determined andthe measuring results are directly used for controlling the formingdevice, said apparatus comprising the uncoiling device for uncoiling thewire from a spool or a coil, and the guiding assembly for feeding thewire towards a forming device for the winding of said wire characterizedby the formation of a loop of the wire between the uncoiling device andthe guiding assembly, by a recognition unit located next to said loopfor measuring a lateral deflection of the wire loop, and by a wirepull-off guide of the uncoiling device arranged rotatably around thespool or coil axis and controlled by the recognition unit to carry outan additional movement, and wherein the recognition unit comprises twosensors located on both sides of the wire loop that create signals whenthe wire loop is laterally deflected, the signals controlling a swivelmovement of the rotatable uncoiling device around an axis parallel tothe wire pull-off direction.